DocumentCode :
1463536
Title :
Optimizing motion-vector accuracy in block-based video coding
Author :
Ribas-Corbera, Jordi ; Neuhoff, David L.
Volume :
11
Issue :
4
fYear :
2001
fDate :
4/1/2001 12:00:00 AM
Firstpage :
497
Lastpage :
511
Abstract :
All motion-vectors are encoded with the same tired accuracy, typically 1/2-pixel accuracy, but the best motion-vector accuracies are not known. We present a theoretical framework to find the motion-vector accuracies that minimize the total encoding rate with this type of coder, for the classical case where all motion-vectors are encoded with the same accuracy, and for new cases where the accuracy is adapted on a frame-by-frame or block-by-block basis. To do this, we analytically model the effect of motion-vector accuracy and show that the energy in a block of the difference frame is approximately quadratic in the accuracy of the block´s motion-vector. This energy-accuracy model is then used to obtain expressions for the total bit rate (motion rate plus difference frame rate) in terms of the blocks´ motion accuracies and other key parameters. Minimizing these expressions leads to simple formulas that indicate how to choose the best motion-vector accuracies for this type of coder. These formulas also show that the motion accuracy must increase where more texture is present and decrease when there is much scene noise or when the level of compression is high. We implement several entropy and MPEG-like video coders based on our analysis and present experimental results on synthetic and real video sequences. These results suggest that our formulas are accurate and that significant bit rate savings can be achieved when our optimization procedures are used
Keywords :
data compression; entropy codes; image sequences; image texture; motion compensation; optimisation; video coding; MPEG-like video coders; block-based motion compensation; block-based video coding; difference frame rate; encoding rate; energy-accuracy model; entropy coding; entropy video coders; image texture; motion rate; motion-vector accuracy optimization; real video sequences; scene noise; synthetic video sequences; total bit rate; video compression level; Bit rate; Encoding; Entropy; Layout; Motion analysis; Noise level; Transform coding; Video coding; Video compression; Video sequences;
fLanguage :
English
Journal_Title :
Circuits and Systems for Video Technology, IEEE Transactions on
Publisher :
ieee
ISSN :
1051-8215
Type :
jour
DOI :
10.1109/76.915356
Filename :
915356
Link To Document :
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